Short wave radio apparatus



March 27, 1934.

F. H. KROGER SHORT WAVE RADIO APPARATUS Filed April 15, 1929 INVENTOR FRED H. KROGER BY W ATTORNEY patented Mar. 27, 1934 PATNT OFFICE SHORT WAVE RADIO APPARATUS Fred H. Kroger, Ridgewcod, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application April 15, 1929, Serial No. 355,117

Claims.

This invention relates to radio apparatus and in particular to radio apparatus to be utilized in communication at short wave lengths, as for instance, 100 meters or less.

' In communicating at radio frequencies below 100 meters it is well known that great diiiiculties are encountered in obtaining apparatus which is stable in operation and which the frequency of the signal oscillations handled can be kept constant or approximately constant. Es-

pecially is this true where high power apparatus is used.

These difficulties are due in part to the inabili-= ty to balance the apparatus with respect to 15, ground and to properly neutralize said apparatus when balanced for all operating voltages and frequencies. These defects are due to a large extent to distributed capacity of the leads to each other and to ground. For the purpose of 10] balancing the apparatus with respect to ground and for other obvious reasons it is desirable to use apparatus inherently symmetrical with respect to ground and to maintain the leads between elements or the apparatus as short as possible.

Briefly and broadly, the primary object of this invention isto provide a novel transmitting circult and apparatus therefor in which the tuning elements oithe circuits are so arranged and constructed as to necessitate a minimum amount of lead wire between the tuning elements and the other apparatus used.

Another object of this invention is to provide such a device in which the circuits and tuning elements are in themselves symmetric with respcct to ground.

These objects are obtained in the present invent-ion by the use of a balanced transmitter arrangement consisting of a master oscillator coupled to the input circuit of a thermionic ampliher which preferably comprises a pair oi thermionic tubes in push-pull arrangement. The output circuit of this push-pull stage is symmetricaliy" balanced with respect to ground and is coupled in any known manner to a load circuit, as for instance, an antenna circuit. According to the present invention, the necessary neutrali ing condensers, the tank condensers, and the variable tuning elements for the tank condenser are combined in one unit necessitating only the two 50. leads "to theplate and the two leads to the grid.

In this manner the distributed capacity to ground is reduced to a minimum.

In apparatus constructed in accordance with this invention the anode side of the tank con- .idenser which is fixed functions also as the plate (Cl. ZED-17) of the corresponding neutralizing condenser. other plate of this neutralizing condenser win h is connected to the grid of the opposed the tank condenser to allow the optimum condenser to be obtained. In like manner, the anode side of the tank condenser associated with the other thermionic tube is capacitively coupled to the grid oi the first named tube through a plate adjustabie with reference to the anode element of the tank condenser, while, the tank condenser c"; is completed through a pair of electrically nn 7d plates, adjustable with respect to said .sed plate elements.

()ne advantage to be gained with a device constructed in accordance with my invention lies in the fact that although an element of the tank condenser is also common to the neutralizing condenser either the tank condenser or the neutralizccndenser may be tuned without altering the in ing of the other.

Another advantage to be gained by theuse of a combined condenser constructed in accordance with the present invention is that the apparatus itself is symmetrical with respect to ground. This renders the apparatus especially desirable in arrangements in which thermionic tubes in pushpull arrangements are used in the'amplifier stage.

Gther advantages will become apparent from the specification, and, therefore, when read in connection with the accompanying drawing in which the single figure illustrates the at present preferred form of my invention.

Referring in particular to the drawing, the condenser arrangement provides a pair of fixed plates 1 2 supported on insulating pedestals- 3 and i. The plate 1 is capacitive coupled to 2 through the variable condenser plates 5 6 carried by threaded rods '7 and 8 rotatably mounted in. a metal sleeve 9 carri d on an insulating support 10. The sleeve 9 is provided internally with right and left hand threads so that when the sleeve is rotated in one direction, plates 5 and. 6 approach plates 1 and 2 respectively, thereby increasing the capacity of the condenser formed by plates 1, 5, 6 and 2. Likewise, when the sleeve 7 is rotated in the opposite direction the plates 5 and 6 are separated from plates 1. and 2 respectively, thereby, reducing the capacity or" the condenser formed by plates 1, 5, 6, and 2.

The plate 1 is connected to the anode 10 of thermionic tube A while the plate 2 is connected to the anode ll of thermionic tube B. Plates 1 and 2 in series with 5 and ii are in parallel with the center tapped inductance 12 in the output circuit of thermionic tubes A and B and provide the tank condenser effect required in this tank circuit. The output circuits of amplifier tubes A and B are completed through a power source 13 and a radio frequency choke 14 to the filament heating circuit 15, which includes a power source 16.

To prevent oscillations being set up in the various circuits, the plate electrode of thermionic tube A is capacitively coupled to the grid of thermionic tube 3 through the capacity effect between condenser plate 1 and condenser plate 17 which is connected to the grid 18 of thermionic tube 3. Condenser plate 17 is mounted for adjustment on a screw is rotatably supported in a journal 20 carried by the insulating support 21. The capacity effect between plates 1 and 17 may be varied by rotating the insulated knob 22 in the desired direction.

The neutralizing effect is completed by capacitively coupling the grid 23 or" thermionic tube A to the plate electrode of thermionic tube B by means of the condenser enect between neutralizing condenser plate 24 and the plate 2 which is connected to the plate electrode of thermionic tube B. Plate 24 is mounted for adjustment on a screw 25 'rotatably mounted in a journal 26 mounted on an insulating support 27. The capacity eifect between plates 2 and 24 is varied by rotating insulating knob thereby, increasing or decreasing the distance between plates 2 and 24.

Oscillations at the desired frequency are supplied to the input circuit of the amplifier through a winding 30 in the output circuit of the master oscillator MO coupled to a center tapped inductance 32 in the input circuit of the amplifier. The input circuits of thetubes A and B completed by connecting the center tap of inductance 32 to the filament circuit 15. This master oscillator has been, for purpose of illustration, shown diagrammatically, as it will be understood that a crystal controlled oscillator or any other well known type of oscillator in general use today may be used. The input circuit including the inductance 32 and variable capacity 33 is tuned by means of 33 to the frequency of the oscillations in the master oscillator. These oscillations are set up alternately between the grid 23 and filament 15 of A and grid 18 and filament 15 of B and are consequently repeated in the output circuit oi the push-pull amplifier. This output circuit as pointed out above consists of an inductance 12 tuned by means of tank condenser 1, 5, 6, 2 to the frequency of the master oscillator. The load circuit which may consist of an antenna system or transmission lines is coupled by means of inductance 35 to the inductance in the plate circuit of the amplifier stage.

To further insure symmetry of the apparatus with respect to ground the filament circuit 15 is grounded at G.

As will be obvious from an inspection of the drawing in apparatus arranged in accordance with the present invention a minimum amount of wire is necessary for connecting the grids and plates of the thermionic tubes to the combined neutralizing and tank condenser. Furthermore, this apparatus which besides being symmetrical itself with respect to ground allows the transmitter circuits to be arranged so that all circuits are symmetrical with respect to ground, and also, provides means for damping out any subsidiary oscillations which may appear in the various circuits.

As the operation of the device will be. apparent from inspection and from the prior description of the arrangement a statement of the operation thereof is thought not necessary.

Although for purposes of illustration I am showing the at present preferred form of my invention and the operation thereof I do not wish to limit myself thereby except as marked out in the claims appended hereto.

I claim:

'1. A condenser comprising a pair of supports, a pair of fixed plates carried thereby, a pair of movable plates mounted adjacent each of said fixed plates, and means for adjusting the distance between each plate of said pairs of movable plates and the adjacent fixed plate.

2. A condenser comprising a fixed plate, a plurality of movable plates, each insulated from said fixed plate and from each other and vcoaxially located with respect to said fixed plate, and means for imparting individual axial movement to each of said movable plates.

3. A low loss compound condenser for use in short wave work comprising, a plurality of fixed plates mounted in axial alignment, a plurality of movable plates adjacent each fixed plate, said movable plates being mounted coaxially with respect to said fixed plates, and means for imparting axial movement to each of said movable plates.

4. Thermionic relaying means comprising, a pair of thermionic tubes having input electrodes adapted to be energized in opposition, an inductance connected between the anode electrodes of said tubes, and means for tuning said inductance and for compensating for inter-electrode capacity in said tubes including, a fixed plate connected to each anode electrode, an axially movable plate mounted adjacent each of said fixed plates, each of said movable plates being connected to the input electrode of one of said tubes, and a second axially movable plate mounted adjacent said fixed plates, said second named movable plates being conductively connected, all of said plates being mounted on a common axis.

5. Signalling means comprising, a pair of thermionic tubes having control grid, and cathode electrodes adapted to be connected in a resonant circuit, a tank circuit connected between the anodes of said tubes, said tank circuit including an inductance and means to tune said inductance to the desired frequency comprising, a fixed plate connected to each anode electrode, a pair 

